This invention generally relates to a technology for automatically detecting multiple sheets of print media.
Laser printers and copiers are common examples of electrophotographic production devices. In general, the art of electrophotographic production devices (EPDs) is well known. One common problem regarding EPDs is the fact that if a printer erroneously pulls multiple sheets of print media into the printer at one time, the result is either poor print quality or a media jam somewhere within the printer, which can be difficult to remedy.
The focus herein is on one component of EPDs: the registration assembly. Traditionally, the role of the registration assembly is to deskew (i.e., straighten or square up) the print medium before an image is printed on it.
Just before the print medium passes through the imaging area of a printer, the printer stops the medium at an internal portion of the printer called the xe2x80x9cregistration assembly.xe2x80x9d One implementation of the registration assembly includes a movable xe2x80x9cstopxe2x80x9d that pops up and literally stops the progress of the medium through the printer. Another registration assembly implementation includes a pair of rollers, one typically a hard material, like steel, and the other a softer, rubber coated roller, which are pressed together to form a contact area, or nip, and can be made to rotate or can be prevented from rotating. The printer forces the leading edge of the paper into either the stop in the first implementation or the stopped pair of rollers in the second implementation, which deskews (i.e., squares up) the paper. Thus, the registration assembly is responsible for ensuring that the paper travels straight into the fuser unit of the printer where the imaging process is performed. If the printer could detect when multiple sheets of media are fed into the registration assembly, remedial action could be taken to prevent poor print quality or a media jam that is difficult to remove.
The following U.S. Pat. Nos. include a general description of an EPD and/or the role of the registration assembly of such a device: 5,865,121; 6,201,937; and 5,967,511.
Described herein is a technology for automatically detecting the presence of multiple sheets of print media. More particularly, described herein is a technology for indirectly and automatically determining when multiple sheets of print media are fed into a printer. In the described embodiment, this is accomplished by determining the stiffness of the fed print media.
At least one embodiment, described herein, includes a laser printer registration assembly. In this assembly, the print medium is deflected (i.e., bent, bowed, buckled, etc.). A measurement of such deflection is made. That measurement is an indication of the relative stiffness of the print medium. A deflection measurement of subsequently fed print media is compared to a previous deflection measurement. If a subsequent measurement is greater than, or more specifically, significantly close to an integer multiple of, a previous measurement, then it is determined that multiple sheets have been fed to the printer.
By determining when multiple sheets are fed into the printer, the print process can be aborted, preventing poor print quality or a physical jam.
This summary itself is not intended to limit the scope of this patent. Moreover, the title of this patent is not intended to limit the scope of this patent. For a better understanding of the present invention, please see the following detailed description and appending claims, taken in conjunction with the accompanying drawings. The scope of the present invention is pointed out in the appending claims.